1. Field of the Invention
The present invention pertains to method and apparatus for welding members together, and more particularly relates to an induction heating and pressure welding method and apparatus wherein an induction heating coil is disposed between weldable surfaces to first heat the surfaces to a welding temperature and then rapidly removing the coil from between the surfaces allowing the surfaces to be forced together to upset the heated metal and provide a high strength, repeatable weld.
2. Description of the Prior Art
Two members to be welded together, for example, members used in the construction of booms of the lattice type for cranes or the like, require accurately machined weldable faces which are flat with V-shaped external grooves to provide the most desirable joint geometry that has been found to produce the best fusion welds. The tubing available for such use frequently vary in thickness and ovality, thereby presenting joint variations which result in detrimental variations in the fusion weld joint. Also, the fusion welding is done under the discretional control of the welders who produce other variables to the fusion welding process. These joints must be tested by ultrasonic techniques and must either be passed or be designated unacceptable and be repaired, thus resulting in very expensive joints because much operator skill, experience, care and time is required to obtain satisfactory joints.
Known prior art welding processes include the following:
The extremely old blacksmith process which includes heating of iron or steel members to their forging or plastic state, bringing the two members together and then applying force or pressure to the two members, as by hammering or the like to provide the weld. One of the problems with this type of welding is that it is very operator dependent and very inconsistent.
Flash welding, resistance welding and arc and butt welding all requires that the two elements are first separated by an air gap. A heavy duty electrical circuit with very large current capacity is then connected to both members and the surfaces to be welded are brought together to cause arcing for a sufficient time to arrive at the welding temperature at which time the current is stopped and the two members are forced together to provide the weld.
Friction welding and inertia welding basically involve holding one member stationary and rotating the other member. The two members are brought together causing frictional heat which raises the contacted surfaces to at least the plastic temperature. Rotation is then stopped and higher axial force is applied to weld the two members together.
Magnetically impelled arc butt welding is similar to flash welding but additionally includes energizing solenoid coils placed around the members to be welded causing the arc to rotate about the centerline of the members being welded which improves uniformity of heating.
Radial friction welding is somewhat similar to friction and inertia welding but includes a third rotating element. The third element is subjected to very high radial forces causing a ring of heated plastic material to reduce in diameter but grow axially. The axial growth creates the axial force which causes the friction heat, and when at the correct temperature the rotation is stopped and a higher radial pressure is applied to weld the members together.